Color television system



Patented Mar. 2,

COLOR TELEVISION SYSTEM Harry S. Bamford, Glenside, Pa., assignor to Farnsworth Television and Radio Corporation, a corporation of Delaware Application August 14, 1941, Serial No.'406,743

7 Claims. (01. 178-52) This invention relates to color television systems wherein picture signals representative of different colors are employed, and, more particularly relates to such systems in which successive signals representative of difi'erent colors are developed for successive fields of an interlaced scanning pattern by means capable of storing electrical charges. I

Picture-signal generating tubes of the storage type which are capable of converting a light image to be transmitted into a corresponding image of electrical charges stored over predetermined time intervals are well known in the art. In accordance with conventional practice, such charge images are scanned by means of an electron beam or a fine beam of light in accordance with a predetermined scanning pattern, thereby to neutralize the stored charges and cause a picture signal to be produced.

The electrical charge image developed in such a tube is usually scanned in accordance with an interlaced scanning pattern. In such a pattern interstices lie between the successive lines of each scanning field and the charge image on these interstices is untouched so that the charges are not neutralized by the scanning beam. These charges thus remain on the interstices between the scanned lines until these interstices are scanned in the succeeding scanning field. If it is desired to transmit pictures in natural colors by means of a charge-storage tube, such as described above, with the picture signals representative of difierent colors developed in successive fields of an interlaced scanning pattern, it is necessary to change the color of the light image, to which the charge image corresponds, during successive fields of the interlaced scanning motion. This maybe accomplished by changing the image light from one color to another ,in synchronism with the motion of the scanning beam, thereby to take advantage of the full time available for electrical charge storage between recurring scansions. A difiiculty then arises, however, in that the elemental areas of the electrical charge image disposed in the interstices between the scanning lines of one field are not neutralized and still carry charges representative of one color component of the image when they begin to accumulate charges representative of another color component of the image to be transmitted. In this manner a picture signal representative of a single color component only is not obtainable, and the color quality of the reproducing image j greatly impaired.

Anobiect of the present invention, therefore,

is to provide a new and improved method and means for generating a color television signal. More specifically, it is an object of the present invention to provide an improved method and means of the character described for developing picture signals representative of single different color components for successive fields of an interlaced scanning pattern.

In accordance with the present invention there is provided a color television signal generating system for developing picture signals representative of difierent colors for successive fields of an interlaced scanning pattern which comprises means including a target for converting the light image to be transmitted into an electrical charge image. An output circuit in which the picture signals are developed is coupled to the imageconvertlng means. Means are provided for scanning the charge image with a first medium of predetermined characteristics in accordance with the interlaced pattern to develop a picture signal in an output circuit. Means are also provided for changing the color of the image light progressively in synchronism with the scanning motion of the first medium. A second scanning means is provided for scanning the interstices of the successive interlaced scanning patterns on the charge image with a second medium having different predetermined characteristics and following the first scanning motion in fixed relationship thereto, thereby to neutralize the remaining charges of the charge image after the scanning by the first medium. An interference signal having a distinctive characteristic is thereby incidentally developed in the output circuit and selective means are coupled to this circuit for transmitting the picturesignal independent of the interference signal.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the accompanying drawing Fig. 1 is an illustration aiding the explanation of the operation of the invention while Fig. 2 shows a schematic drawing of a preferred embodiment thereof.

Referring now more particularly to Fig. 1 of the drawing, there is shown schematically a photoelectric mosaic I on which an image of a cross 2 is focused. In front of the mosaic I there is disposed a color-filter disc 3 of which a fragment only is shown, having a red-color filter section 4 and a green-color filter section 5 and rotat- 01 a light beam or an electron beam is indicated at I, scanning the lines-of the odd-line field indicated by the shaded strips 3 from left to right' I and top to bottom. It can be seen from the drawing that the interstices 8 between the strips 3, representing the even lines, are not scanned by the beam 1 during the odd-line field and the charges thereon are notneutralized. Hence, as

the color of the image of cross 2 changes from red to green, charges representative of the green component of the image, except for the arrangement hereinafter described, would begin to accumulate in the interstices 9 upon the charges already accumulated which are representative of the red component. In order to avoid this undesired mixing of colors, however, the even lines are scanned by a scanning beam indicated at l which follows the scanning beam 1 and neutralizes the charges remaining in the charge image after the scanning by the first beam. Hence, when the image color changes from red to green, the mosaic is completely neutralized over the area in which this change takes place and therefore the charges which are then accumulated thereon are representative of the green color component only.

Since the second scanning beam l0 also incidentally develops an interfering picture signal, it is desirable to provide this signal with a distinctive characteristic so that the desired picture signal may be selected from the composite of the two combined signals which is developed. For

this purpose, in accordance with the present invention, the intensity of the second scanning beam I0 is modulated in response to a signal having a frequency higher than the highest picture signal frequency, thereby to provide it with a distinctive characteristic.

While color sections 4 and of the filter 3 have been shown as touching each other along a line 6, this is not-essential to the invention since there may well be a strip therebetween which is opaque to light so that the image light does not change directly from one color to another.

In Fig. 2 there is shown a color television signal generating system in accordance with the present invention, which comprises a picture signal generating tube 2| having a bulb portion 22 and neck portions 23 and 24. For the purpose of converting the light image into an electrical image, there is provided a mosaic target 25 of conventional construction comprising a signalplate 26, a layer of insulating material 21, a photoelectric mosaic 28, and a lens system schematically indicated at 29 capable of projecting an optical image of the object 33 to be transmitted upon the photoelectric mosaic 28. For changing color of the image light of the image to be transmitted, in successive fields of the interlaced scanning pattern, there is provided a color filter disc 3|, preferably comprising sections of red, blue and green filters positioned in front of the photoelectric mosaic 28. The disc 3| is driven by a motor 32 which may be of the phonic-wheel type held in synchronism with the scanning of the interlaced pattern by means of synchronizing pulses applied to the terminals so labelled.

For the purpose of scanning the electrical charge image with an electron beam 23A to develop a picture signal,

tube neck portion 23 of tube 2| an electron gun of conventional design comprising an indirectly heated cathode 35, a control element 36, a first anode 31, a focusing electrode 33 and a second anode 39, the latter preferably extending into the bulb portion 22 of the tube envelope, all held at suitable operating potentials by means of a voltage source schematically indicated as a battery 43.

For horizontal deflection of the scanning beam 23A across the photoelectric mosaic 28 there are provided a pair of defl'ecting plates 42 connected to a source of deflecting voltage 43 .while a pair of deflecting plates 44 connected to a source of deflecting voltage 45 are provided for vertical deflection of the scanning beam.

Similarly, a second electron gun comprising an indirectly heated cathode 46, a control element 41, a first anode 48, a focusing electrode 43, and a second anode are provided in the tube neck portion 24 of tube 2| for developing a second scanning or neutralizing beam 24A. The'second anode 50 preferably also extends into the bulb portion 22 of the tube 2| and is joined with the secondanode 39 therein to form a unitary structure. The elements of the electron gun just described are held at suitable operating potentials bymeans of a voltage source schematically indicated as a battery 44. Two pairs of deflecting plates 5| and 52 connected to deflecting voltage supplies 53 and 54, respectively, are provided for horizontal and vertical deflection of the electron beam 24A. Since the axes of the undeflected electron scanning beams 23A and 24A intersect the mosaic 23 under oblique angles the scanning waves are supplied to the deflecting plates with proper shape to compensate for keystone distortion.

For the purpose of modulating the scanning beam 24A there is provided a modulation-signal generator 55 coupled to the control element 4'I by means of a condenser 56 and a resistor Fl connected in circuit as shown. A resistor 53 is connected to the signal plate 26 of the mosaic screen 25 in the output circuit of the tube. Coupled to this resistor, as shown, is a frequency there is provided in the selective filter 59 preferably of the low-pass type transmitting only the picture signal frequencies.

In the operation of the system, an optical image of the object 30 is focused .by the lens system 29 upon the photoelectric image 23 thereby converting the light image into a corresponding electrical charge image. The charge image is scanned by means of the scanning beam 23A which isof constant intensity and is deflected in horizontal and vertical directions by means of deflecting plates 42 and 44, respectively, thereby to develop a picture signal across the output resistor 58.

The color filter disc 3| is rotated by means of the motor 32 in synchronism with the movement 'of the color of the light thereon. In scanning the mosaic 28 with the beam 24A the remaining charges of the charge image after the scanning with the beam 23A are neutralized and incidentally an interfering signal is developed. The

scanning beam 24A is modulated in accordance with a signal developed by the modulation-signal generator 55 which may be a sinusoidal oscillation having a frequency in the order of megacycles.

In accordance with present-day television standards, the picture signal generally encom passes a frequency range between approximately 30 cycles and 4 megacycles Hence, the modulated beam 24A develops an interference signal in the output resistor 58 which covers a frequency band of between 6 and 14 megacycles considering the modulation of a 10 megacycle carrier by a maximum modulation frequency of 4 megacycles. The two frequency bands of the picture signal and the interference signal range 1 from 30 cycles to 4 megacycles and 6,to 14 megacycles and can, therefore, readily be separated characteristics in accordance with an interlaced scanning pattern to develop a picture signal in laced scanning pattern on said charge image with with any further separate frequency selective means, since the output circuit per se may have sufliciently strong frequency discriminating characteristics.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention,

What is claimed is:

1. A color television system for developing picture signals representative of difierent colors, in successive fields of an interlaced scanning pattern, comprising means for converting the light image to be transmitted into an electrical charge image, an output circuit coupled to said converting means, means for scanning said charge image with a first medium of predetermined characteristics in accordance with an interlaced scanning pattern to develop a picture signal in said output circuit, means for chang ing the color of the image light progressively in synchronism with the scanning motion of said first medium, means for scanning the interstices in said interlaced scanning pattern on said charge image with a second medium having different predetermined characteristics following said first-named scanning motion in fixed relationship thereto to neutralize the remaining charges of said charge image after the scanning thereof by said first medium and thereby incidentally developing an interference signal in a beam of electrons having different predetermined characteristics following the scanning motion of said first-named electron beam to neutralize the remaining charges of said charge image after the scanning thereof by said first beam and thereby incidentally developing an interference signal in said output circuit havinga distinctive characteristic, and selective means coupled to said output circuit for transmitting said picture signal independent of said interference signal.

3. A color television system for developing picture signals representative of different colors in successive fields of an interlaced scanning pattern, comprising means for converting the light image to be transmitted into an electrical charge image, an output circuit coupled to said'converting means, means for scanning said charge image with an unmodulated beam of electrons in accordance with an interlaced scanning pattern to on said charge image with a modulated beam of electrons following the scanning motion of said unmodulated beam in fixed relationship to neutralize the remaining charges of said charge image after the scanning by said unmodulated beam and thereby incidentally developing an interference signal in said output circuit having a distinctive characteristic, and selective means coupled to said output circuit for transmitting said picture signal independent of said interference signal.

4. A color television system for developing'picture signals representative of different colors in successive fields of an interlaced scanning pattern, comprising means for converting the light image to be transmitted into an electrical charge image, an output circuit coupled to said converting means, means for scanning said charge image with an unmodulated beam of electrons in accordance with an interlaced scanning pattern to develop a picture signal in said output circuit,

means for changing the color of said image light progressively in synchronism with the scanning motion of said electron beam, means for scanning the interstices in said-interlaced scanning pattern on said charge image with a modulated beam of electrons following the scanning motion of said unmodulated beam in fixed relationship to neutralize the remaining charges of said charge image after the scanning thereof by said unmodulated beam and thereby incidentally developing an interference signal in said output circuit having a distinctive characteristic, the modulation frequency of said modulated beam being higher than the highest frequency component of said picture signal, and selective means coupled to said output circuit for transmitting said picture signal independent of said interference signal.

5. .A color television system for developing picture signals representative of different colors in successive fields of an interlaced scanning pattern, comprising means for converting the light image to be transmitted into an electrical charge image, an output circuit coupled to said converting means, means for scanning said charge image with an unmoduiated beam of electrons in accordance with an interlaced scanning pattern to develop a picture signal in said output circuit, means for changing the color of the image light progressively in synchronism with the scanning motion of said electron beam, means for scanning the interstices in said interlaced scanning pattern on said charge image with a modulated beam of electrons following the scanning motion of said unmodulated beam in fixed relationship to neutralize the remaining charges of said charge image after the scanning'thereot by said unmodulated beam and thereby incidentally developing an interference signal in said output circuit having a distinctive characteristic, the modulation frequency of said modulated beam being higher than the highest frequency component of said picture signal and said output circuit having a frequency characteristic adapted to pass said picture signal only.

6. In the art of color television, the method A of developing picture signals representative of different colors in successive fields of an interlaced scanning pattern, which comprises the steps of converting the light image to be transmitted into an electrical charge image, scanning said charge image with a first medium of predetermined characteristics in accordance with an interlaced scanning pattern to develop a picture signal in an output circuit, changing the color 4 of the image light progressively in synchronism with the scanning motion of said first medium,

of developing picture signals represenative of different colors in successive fields of an interlaced scanning pattern, which comprises the steps of converting the light image to be transmitted into an electrical charge image, scanning said charge image with an unmodulated beam of electrons in accordance with an interlaced scanning pattern to develop a picture signal in an output circuit, changing the color of the image light progressively in synchronism with the scanning motion of said first medium, scanning the interstices in said interlaced scanning pattern on said charge image with a modulated beam of electrons foilowing said first-named scanning motion in fixed relationship thereto to neutralize the remaining charges of said charge image after the scanning thereof by said unmodulated beam and thereby incidentally developing an interference signal in said output circuit having a distinctive characteristic, and transmitting said picture signal independent of said interference signal.

HARRY s. BAMFORD. 

